How do I use Shrinkwrap Modifer with more control?
Shrink Wrap with Vertex Group Weights

By using vertex groups modified in weight paint you can exert more control.





A the very flat square box begin as a cube Mesh. Subdivided as seen, High Vertex Density. I will call it a box. Left to Right parts of the image -->


For simple models you can consider texture painting.  I tend to think you do not want this.
On the left the box is showing weights in edit. Painting occurred in Weight Paint Mode.  You can see vertex group names.  A Mesh can have many vertex groups. All hidden vertices are zero weight.
Next the box with NO modifiers
Next the box with Shrink Wrap Modifier ..and vertex group specified ... Note the red weights allow the vertices to move the most. The top of the box is stable and does not move, this is the control weight paint efforts allow.  Lets call this [Context 1]
Next the box with Shrink Wrap Modifier ... No Vertex group .. it collapses to where many faces are close to each other .. lack of control
Next same as in [Context 1] but the inverse of the group has been selected.  Only the red paint area stays in it original place. Weight of Vertex X is now (1 - original weight)
Consider adding a second or more Shrink Wrap modifier your waist area.  


Notes




A flexible fabric in daily life conforms to a body.  Stretch Fabric even more.
A bullet proof vest and bomb squad disposal suit might conform very little.
You must use your judgement.  Breaking a model in to flexible and inflexible parts should be considered one of your tools, along with others.
Practice simple cases of Weight Paint and ShrinkWrap.  Improve the example you see here.
Weight Paint mastery is an essential skill for Shrinkwrap.
Once you have control over the vertex group weights you can make more informed decisions.
Then see more advanced tutorials.
This is just a quick highlight. This topic requires further research.